Method for determining the rates of motion and wheel for roller skates and skateboard

ABSTRACT

A wheel for roller skates or roller boards, the wheel having a non-rotating axle of rotation and a wheel body rotatable around an axle of rotation, the wheel includes means for measuring the speed at the wheel and means in the wheel for determining its rate of rotation and/or the actual rate of travel of a user of the roller skate or roller board or other sports equipment containing the wheel.

FIELD OF THE INVENTION

The present invention relates to a method to determine travel quantitiesand an associated wheel for roller skates and roller boards.

BACKGROUND OF THE INVENTION

Sports equipment for fitting to the feet, for example inline skates,roller skates, grass skis, skateboards or snakeboards, are becoming moreand more popular. There is a need to determine the sports achievementsperformed with such sports equipment, for example the distancestravelled or the speed reached (current speed, maximum speed, averagespeed).

A bicycle is known from U.S. Pat. No. 4,689,557 wherein the speedmeasurement can be relised by means located in the wheel axle.

The construction described in this publication can, however, not be usedin the region of the substantially smaller wheels for roller skates androller boards as, for example, the signal generated has to be picked upby means of a very complex signal pick-up construction.

A bicycle is known from JP 62-177 453 A which determines the speed via acyclometer comprising a rotating magnet and a stationary sensor. Themechanism described therein is, however, not suitable for roller skatesand roller boards which are exposed to extreme shock strains.

A road skate is known from DE-GM 92 09 825.8 with a travel computerwhich is fitted to the boot of the road skate. To transfer data fromrollers of the road skate to said travel computer, a friction wheel isprovided which acts together with a driver wheel attached to the rollersuspension. This mechanism is considered very complex and susceptible tobreakdown. In addition, it has a large construction.

It is known from DE-GM 296 06 965 to provide a roller for roller skateswith a magnet and a coil to generate an induced current to feed a lightemitting element. This publication does not deal with the measurement ofachievement parameters of a user.

It is known from DE 44 44 315 A1 to provide on an axle fixed to a rollera dynamo to generate current to operate a light. This mechanism alsoproves to be very complex in practice, with, in addition, a strongfriction force which hinders progress being produced by the dynamo. Thismechanism is not suitable for rollers which revolve around anon-rotating fixed axle.

Finally, a roller skate is known from German utility model DE 296 16 211U1 with a frame, a boot which can be connected to the frame and rollersmounted on or in the frame, in which on one of the rollers a contactmaker is disposed and on the frame a contact pick-up coupled to thetransmitter is disposed, with a receiver equipped with a display fittedfor the display of achievement data, which receiver can be taken alongby the roller skate, being allocated to said transmitter.

OBJECTS AND SUMMARY OF THE INVENTION

It is the object of this invention to provide a wheel for roller skatesand roller boards with which achievement parameters of a user can bemeasured in a simple, robust and favourably priced manner.

In accordance with one advantageous embodiment, the wheel possesses acoil fixed to its non-rotating axle of rotation and a magnet surroundingthe coil concentrically connected to the wheel body. When the wheelturns, the magnet thus rotates around the coil so that a current isinduced in the coil. The induced current is proportional to the rate ofrotation of the wheel. The induced current (or the induced voltage) canbe led in a simple manner to a electronic control means which performs asignal processing. The design with magnet and coil has proved to be veryrobust and compact in construction. Furthermore, there is, wherecircumstances require, no additional battery necessary for the powersupply to the electronic control means. Advantageously, with the currentgenerated, a storage battery can be charged which ensures a directcurrent supply for the electronic control means and/or other components.The storage battery and a rectifier connected in series with it can alsobe integrated in the wheel.

It is conversely also possible to provide a magnet fitted to the axle ofrotation and a coil surrounding the magnet concentrically and connectedto the wheel body.

Appropriately, the wheel comprises means to determine its ground contactand/or means to determine an angle between a momentary touch-down orcontact direction of the wheel and an effective direction of travel ofthe user of the sports equipment. As, for example, in roller skates orinline skates, only one roller skate or inline skate typically hascontact with the ground at any one time, it is possible in this way todetermine the roller skate or inline skate having contact with theground in each case and to determine on this basis the rate of rotationor the rate of travel. Furthermore, by determining the angle between thetouch-down direction of the roller and the actual direction of travel, asubstantially more exact measurement of the actual parameters ofachievement or travel of the user can be performed. This measurementprecision meets an urgent need which has existed for some time, inparticular in the area of high-performance sports.

Advantageously, dynamometers or force-meters, particularly piezoelements, are used to determine the contact with the ground and/or todetermine the angle between the momentary direction of contact of thewheel and the effective direction of travel. Piezo elements of this typeare of very compact construction, are robust and can be located at anumber of points within the wheel or in its direct environment.

Appropriately, at least one piezo element is located in the wheel body,in particular in an external rolling surface of the wheel, to measurethrust and/or to measure a shear force between ground and wheel. Thisarrangement allows an especially exact and reliable measurement. Thenumber of piezo elements arranged on the rolling surface can be varieddepending on the desired demands on the precision.

Appropriately, a number of piezo elements are spread over thecircumference of the wheel body. In this way, it is ensured that anycontact with the ground or any change in direction can be detecteddirectly.

It is further possible in an advantageous manner to provide at least onepiezo element at the axle of rotation, in particular in the region ofaxle suspension means to measure thrust and/or a shear force betweenground and wheel and/or a precession force caused by a change indirection of the wheel. Here, it is of special advantage that the sizeor number of dynamometers or piezo elements can be kept small; inaddition, they are mounted on the non-rotating axle, which leads to lesswear over fitting to the rotating wheel body.

It is further possible to provide at least one piezo element in the axissuspension means and/or on the bearings of the wheel to measure a forceof pressure (pressure force) and/or a shear force between ground andwheel and/or a precession force caused by a change in direction of thewheel. Piezo elements arranged in this way are also of compactconstruction and are less susceptible to wear due to their non-rotatingarrangement.

In accordance with another advantageous embodiment, the wheel possessesa sensor extending between the axle of rotation of said wheel and theground. The sensor attached to the axle of rotation has a length whichis slightly larger than the radius of the wheel so that in the event ofcontact with the ground the sensor can detect this in a certain manner.Spring elements, elastic elements, rigid elements with sprung partialregions, etc. can, for example, be provided as sensors. Optical and/orelectrical devices are feasible to determine the contact with theground.

Advantageously, the sensor possesses at least one dynamometer, inparticular a piezo element to detect the contact with the ground and/oran angle between the momentary direction of contact of the wheel and theactual direction of travel.

Preferably, the sensor is fixed to an extension to the axle of rotationprovided outside the axle suspension. Such an axle of rotation extensioncan be executed with little constructive effort.

Appropriately, the magnet and coil can be integrated in modular fashionas components of a generator in the wheel body, with the generator shaftbeing able to be used as the axle of rotation. This modular-type ofconstruction has proved to be particularly favourable in cost as it canbe inserted in a simple manner into a wheel hollowed out accordingly.The assembly work on the wheel is thus reduced.

Advantageously, the wheel possesses electronic control means integratedin the wheel body. In this way, the signal paths, for example from thecoil or from the piezo elements used, are very short, by which means afast and reliable transfer or processing of data is ensured.

Appropriately, radio connection means are provided for the exchange ofdata with another wheel, in particular a wheel of a second roller skateand/or with a display device, in particular one formed in the manner ofa wrist watch, to display the data determined. In this way, the datadetermined can be displayed to the user in a simple fashion.Furthermore, thanks to the data transfer between single rollers, theessential components of the electronic control means can be providedonly in one roller, with this also processing data transferred fromother rollers.

Advantageously, a current generated via the magnet coil arrangement orvia the generator can be utilised for further functions, in particularto feed a diode rear light connected to the sports equipment. In thisway, the road traffic safety of a roller skate or roller board providedwith the wheel in accordance with the invention is increased. Acousticwarning devices can also be operated in this way.

In accordance with a particularly preferred embodiment of the invention,the means to determine the ground contact possess a device to pick up orrecord a measurement curve describing the rate of rotation of the wheel.When the wheel contacts or is lifted off the ground or surface, such ameasurement curve shows kinks (irregularities in the differentiationfunction of the measurement curve) which can, for example, be detectedby the electronic means integrated in the wheel, by means of which theground contact intervals can be determined in simple fashion. By meansof this measurement curve or its kinks, certain travel states of thewheel can also be detected, for example acceleration, constant travel orbraking. To keep the costs for the fitting of a roller skate or rollerboard with a speedometer device low, preferably only one wheel inaccordance with the invention is provided per pair of roller skates orinline skates. The distance covered by a user during which the boot withthe relevant wheel has no contact with the ground can be extrapolatedfrom the directly preceding measurements.

In accordance with an advantageous embodiment of the method inaccordance with the invention, the ground contact of the at least onewheel is determined at which the rate of rotation and/or the anglebetween its direction of contact and the actual direction of travel isdetected. In this way, an improved precision of measurement is possibleas always only measuring data of a wheel in contact with the ground areprocessed. It is, for example, also possible, in the event of asimultaneous contact of two wheels provided with the measuring devicesin accordance with the invention, to pick up both measurement values andto form a mean value from this. In this way, the measuring precision canalso be further increased.

In summary, the present invention is directed to a wheel for rollerskates or roller boards, with a non-rotating axle of rotation (9, 19)and a wheel body rotatable around the axle of rotation and means tomeasure the speed at the wheel, with means (2, 4, 5, 10) being providedin the wheel to determine its rate of rotation and/or the actual rate oftravel of a user of the sports equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are now described in detail bymeans of the enclosed drawings in which:

FIG. 1 shows a schematic partial sectional view of a first embodiment ofthe wheel in accordance with the invention;

FIG. 2 shows a schematic partial sectional view of the second embodimentof the wheel in accordance with the invention;

FIG. 3 shows a schematic partial sectional view of a third embodiment ofthe wheel in accordance with the invention;

FIG. 4 shows a schematic partial sectional view of a fourth embodimentof the wheel in accordance with the invention;

FIG. 5 shows a measurement curve in which revolutions per second of awheel in accordance with the invention is entered over time; and

FIG. 6 shows in a perspective view a preferred embodiment of a wheel inaccordance with the invention, with the arrangement of the wheel onroller skates and the transfer of measurement data to a display devicedesignated in the manner of a wrist watch are additionally shown by wayof illustration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1 to 4, wheels or rollers 20 are shown which can rotate arounda non-rotating axle 9 or 19. Such wheels are used, for example, onroller skates or inline skates, or also skateboards, snakeboards orgrass skis. The rollers are formed symmetrically around the axles 9, 19so that a presentation of the portion below the axle 9 has been omitted.

In FIG. 1, wheel 20 comprises a wheel body 21 which is provided with arecess in which a permanent magnet 4, a coil 5 and a electronic controlmeans 7 can be inserted.

The electronic control means 7 and coil 5 are here fitted in anon-rotating manner with respect to the non-rotating axle 9. The atleast one permanent magnet 4 is mounted in a non-rotating manner on thewheel body 21 so that it can rotate with this around axle 9. The coil 5is mounted on a coil mount 6.

A protective cap 10 is provided which protects the components insertedin the recess 22 from external influences. The wheel body 21 is mountedvia a bearing 8 in a rotating manner on the axle 9.

A piezo element 2 is located in the running surface 1 of the wheel body21. When a force is applied to the piezo element 2, this generates acurrent (or a voltage) which can be transferred to the electroniccontrol means 7 via lines and a wiper contact 3.

The piezo element 2 can be used to measure a force of pressure todetermine the contact with the ground of the wheel 20 and/or todetermine a shear force between ground and wheel.

Force of pressure occurs when strain is put on the wheel 20, i.e. whenthe weight of the user is put on the roller skate or inline skateconnected to the wheel 20. A shear force occurs when the touch-downdirection of the wheel does not correspond to the actual direction oftravel of the user. Such an angle between the touch-down direction andthe direction of travel occurs in particular frequently with rollerskates and inline skates as here preferably the so-called “ice-skatingstep” is used to effect progress. It is possible to locate several piezoelements 2 in the running surface 1 with certain piezo elements 2 beingable to measure the force of pressure and other piezo elements the shearforce.

When the wheel 20 turns or rotates, the magnets fixed to the wheel body21 orbit around the coils attached in a fixed manner to the non-rotatingor rigid axle 9, with a voltage dependent on the rotational speed of theroller being induced in said coils. Via an A/D converter and a controlfunction, the generated voltage is allocated a rotational speed fromwhich, the roller diameter being known, the distance the wheel hascovered is determined. It should be mentioned here that this measurementmethod can also detect a backwards motion of the user.

Since, as described, when travelling, the roller skates or inline skatesare not always put down in the direction of travel (ice-skating step),the distance covered by the wheel does not correspond to the actualdistance of the user or the roller skater or inline skater. Tonevertheless determine the actual travel distance, the angle betweenboot and direction of travel is determined by means of piezo elements 2,as is information on the ground contact of the wheels 20. These data arealso transferred to the electronic control means 7, in particular via awiper contact 3.

FIG. 2 shows another embodiment of the wheel in accordance with theinvention. Identical components are provided with the identicalreference numbers to FIG. 1. The embodiment of FIG. 2 essentiallydiffers from that of FIG. 1 in that the dynamometer or piezo elements 2in the non-rotating axle 9 are integrated at the height of at least oneaxle suspension means 13. The forces acting upon the roller 20, whichwere described, for example, with reference to FIG. 1, are transferredto the piezo elements arranged in the suspension means 13 via the axle9. In addition to the measurement of a pressure-force or a shear force,piezo elements arranged in this way are also able to measure precessionforces or gyroscopic forces. If, namely, the wheel 20 is considered as agyroscope, a change in direction of the roller skate or inline skate,that is also a change in direction of the axle of rotation 9, is thenequivalent to an artificial precession. Depending on the degree of thechange of direction, more or less strong bearing forces can be observed.Said bearing forces accordingly depend on the strain of the wheel 20 andthe angle between the direction of contact and the actual direction oftravel, with additional precession forces being able to be usedadditionally here for the measurement.

In this connection, it is possible, for example, for the purpose ofsimplification of the data processing, for the manufacturer to recordmeasuring series corresponding to different angle positions and/ordifferent angle changes and to program these into the electronic controlmeans. In this way, force quantities actually measured can be comparedwith the measuring series values in which way a simplification of thedata processing is possible.

The non-rotating arrangement of the piezo elements 2, in particular inthe region of the axle suspension means, allows the size or the numberof piezo elements to be kept very small. In addition, in this way themechanical strain or the wear of the piezo elements can be reduced.

Another embodiment of the wheel in accordance with the invention isshown in FIG. 3. Here, too, identical components are identified with thesame reference numbers.

Here, instead of the transfer of force via the roller body 21 and theaxle 9, a transfer of force is performed via a sensor 11 to piezoelements 2. The sensor 11 is fitted to an extension of the axle 9provided outside the axle suspension means 13. The length of the sensoris slightly larger than the radius of the wheel so that any groundcontact of the wheel 20 can always be detected via the sensor 11. Inaccordance with the embodiments already described, forces of pressureand shear forces can be transferred to the correspondingly positionedpiezo elements via the sensor 11 so that the required data processingessentially corresponds to that already described.

The sensor can, for example, be defined in the form of an elastic orflexible lamellar or brush-like element. It can furthermore be formed asan essentially rigid rod with an elastic end region. Particularly,preferred is the measurement of ground contact and travel angle by meansof two piezo elements 2.

FIG. 4 shows another embodiment of the wheel in accordance with theinvention. Here, the elements used to generate the current or voltage,i.e. permanent magnet and coil, are fitted in a generator 14 in modularform. The shaft of the generator 14 can here be used as a non-rotatingshaft 19 of the wheel. If the generator 14 is inserted in acorresponding recess in the roller body 21, depending on the designaspect of the generator as an outer pole generator or an inner polegenerator, either the permanent magnet or the coil is connected in anon-rotating manner to the generator axle 19. The housing of thegenerator 14 together with the other element required in each case togenerate the current, i.e. the coil or the permanent magnet, is pivotedaround the generator axle 19 and can be connected to the roller body 21.When the roller body 21 is turned around the generator shaft 19 servingas the axle of rotation, current or voltage is thus generated in themanner described above.

The piezo elements 2 provided for the measurement of force are formed inthe embodiment shown in FIG. 3 in the axle of rotation 19 at the heightof the axle suspension means. It is, however, also possible to use oneof the other possibilities described to measure the force.

The data determined in each case are evaluated in the electronic controlmeans 7 and transferred, for example, via a radio connection to areceiver on the wrist of the user who has them displayed on a wristwatch-like display. The current generated in accordance with theinvention to measure achievement parameters of a user is also sufficientfor other uses. In particular, it is possible to use the current tooperate a diode rear light fitted to the boots, by means of which safetyin road traffic is increased. A watch or a timer can also be operated inthis way. Here, the user of a storage battery has proved to be ofadvantage, which storage battery evens out and stores the currentgenerated via a rectifier. In this way, the current supply of thelighting can also be maintained during a short standstill of the roller.

With reference to FIG. 5, a preferred method is now described todetermine the travel speed of a roller skater. Here, the measuredrevolutions per second of a wheel are entered against the time. Duringintervals I1 and I4, the revolution speed of the wheel increases. Attimes t1 and t4, the measurement curve shows kinks to which intervals I2and I5 of falling revolution speed connect. It is concluded from thekink behaviour of the measurement curve at times t1, t4 and thesubsequent fall in revolution speed, that at these times the wheel islifted off the ground. During the intervals I2 and I5, the wheel is inthe air. Only at times t2 and t5, which are characterised by a kinkbehaviour and a subsequent rapid increase in the revolution speed, doesthe wheel again come back onto the ground and is subjected toacceleration. Here, the intervals I1 and I4 already mentioned connect tothe phases of strong acceleration (intervals I3 to I6) caused by thetouching down of the wheel. It should be mentioned here that thetransition from I3 to I4 or from I6 to I7 will run more smoothly inpractice than shown in this schematic presentation. Furthermore,intervals I7 and I8 are shown. Interval I7 is a roll-out phase in whichthe revolution speed of the wheel gradually reduces (without any kinkbehaviour). At interval I8, an acceleration out of the roll phaseoccurs, with again no kink behaviour being present, the wheel thereforenot being raised off the ground.

In this connection, is proves appropriate to include or programindividual parameters of a roller skater in the electronic controlmeans. Reference is made here, for example, to the step length ortypical touch-down angle of a roller skater. By using such parameters,the computation effort to be performed by the electronic control meanscan be reduced.

In FIG. 6, finally, another embodiment of a wheel for roller skates androller boards is shown in perspective. Here, wheel 20 possesses a wheelbody 21 formed with a recess 22.

At least one permanent magnet can be integrated in the wheel body 21 ina suitable manner (not shown).

One possible position of a measuring wheel in accordance with theinvention on a roller skate 100 is also shown schematically in FIG. 6.The fixing of the wheel axle 9 to a wheel rail 101 is performed here ina manner known per se and need not be further explained here.

In recess 22, a puck-shaped or cylindrical washer shaped component 30can be inserted or fitted. In this component 30, the electroniccomponents described above to measure the speed at the wheel areinserted. By way of example, a coil 5, resistors or amplifiers 7 a and achip 7 b of the electronic control means 7 are shown schematically.These components are preferably cast or sealed into component 30 whichin particular consists of synthetic resin. Component 30 possesses acentral recess 30 a which, when the component 30 is inserted into therecess 22 of the wheel 20, fits flush with a central recess 21 a formedthere. The non-rotating axle 9 can be fitted through the flush recesses21 a, 30 a. Component 30 can be connected in a non-rotating manner withaxle 9. When the wheel turns, axle 9 and component 30 thus remainnon-rotatory with respect to the rotating wheel 20. By integrating theelectronic components in component 30, a protective cap 10 such as wasprovided in the other embodiments can be dispensed with. Such a designproves to be very robust. Furthermore, the component 30 containing theelectronic control means can be replaced in modular form.

By means of the chip 7 b, measuring values recorded can be transferredby radio to a display device 50 designed in the manner of a wrist watchas also shown schematically in FIG. 6.

While this invention has been described as having a preferred design, itis understood that it is capable of further modifications, and usesand/or adaptations of the invention and following in general theprinciple of the invention and including such departures from thepresent disclosure as come within the known or customary practice in theart to which the invention pertains, and as may be applied to thecentral features hereinbefore set forth, and fall within the scope ofthe invention.

What is claimed is:
 1. A wheel for roller skates and roller boardssports equipment having a non-rotating axle, comprising: a) a wheel bodyfor being rotatably mounted around the non-rotating axle; b) meansdisposed in said wheel body for determining rotational speed of saidwheel; and c) means disposed in said wheel body for determining theactual speed of travel of a user.
 2. A wheel for roller skates androller boards sports equipment having a non-rotating axle, comprising:a) a wheel body for being rotatably mounted around the non-rotatingaxle; b) means disposed in said wheel body for determining rotationalspeed of said wheel; c) means for determining ground contact with saidwheel; d) means for determining an angle between a touch-down directionof said wheel body and an actual direction of travel of a user; and e)means for determining the actual speed of travel of the user from therotational speed of said wheel, the ground contact of said wheel andsaid angle.
 3. A wheel for roller skates and roller boards sportsequipment having a non-rotating axle, comprising: a) a wheel body forbeing rotatably mounted around the non-rotating axle; b) means disposedin said wheel body for determining rotational speed of said wheel; c)means for determining ground contact of said wheel including means forrecording a measurement curve representative of the rate of rotation ofsaid wheel whereby the ground contact is determined from kinks occurringin the measurement curve.
 4. A wheel for roller skates and roller boardssports equipment having a non-rotating axle, comprising: a) a wheel bodyfor being rotatably mounted around the non-rotating axle; b) aninsertable component for insertion in said wheel body in a non-rotatingmanner with respect to the non-rotating axle; and c) said componentincluding means for determining the rotational speed of said wheel bodyand the actual speed of travel of a user.
 5. A wheel for roller skatesand roller boards sports equipment having a non-rotating axle,comprising: a) a wheel body for being rotatably mounted around thenon-rotating axle; b) a transducer mounted in said wheel body to providean output signal proportional to the rate of rotation of said wheel; c)sensor to determine ground contact of said wheel; and d) an electroniccontrol mounted in said wheel body and operably connected to saidtransducer and said sensor to determine the actual speed of travel of auser.
 6. A wheel as in claim 5, wherein: a) said transducer includes acoil and a magnet operably associated with each other such that saidcoil generates an output proportional to the rotational speed of saidwheel.
 7. A wheel as in claim 6, wherein: a) said coil is mounted in anon-rotating manner with respect to the non-rotating axle; and b) saidmagnet is mounted to said wheel body.
 8. A wheel as in claim 6, wherein:a) said coil is mounted to said wheel body; and b) said magnet ismounted in a non-rotating manner to the non-rotating axle.
 9. A wheel asin claim 5, and further comprising: a) another sensor to determine anangle between a touch-down direction of said wheel and an actualdirection of travel of a user.
 10. A wheel as in claim 5, wherein saidsensor includes a piezo element located in an external running surfaceof said wheel body.
 11. A wheel as in claim 5, wherein said sensorincludes a number of piezo elements spread over the circumference ofsaid wheel body.
 12. A wheel as in claim 5, wherein said sensor includesa piezo element provided on the non-rotating axle and in a region of anaxle suspension means.
 13. A wheel as in claim 5, wherein said sensorincludes a piezo element provided in a wheel axle suspension means andwheel bearings of said wheel.
 14. A wheel as in claim 5, wherein saidsensor extends between the non-rotating axle and the ground.
 15. A wheelas in claim 14, wherein said sensor is fixed to an extension of thenon-rotating axle and an exterior of an axle suspension means.
 16. Awheel as in claim 5, and further comprising: a) a generator including amagnet and a coil provided in said wheel body; and b) said generatorincludes a shaft functioning as the non-rotating axle.
 17. A wheel as inclaim 5, wherein said transducer and said electronic control aredisposed in an insertable component for insertion in said wheel body ina non-rotating manner with respect to the non-rotating axle.
 18. A wheelas in claim 17, wherein said insertable component includes a syntheticresin into which said transducer and said electronic control are cast.19. A wheel as in claim 5, and further comprising: a) a wrist watch-likedisplay including a receiver in radio connection with said electroniccontrol.
 20. A wheel for roller skates and roller boards sportsequipment having a non-rotating axle, comprising: a) a wheel body forbeing rotatably mounted around the non-rotating axle; b) a transducermounted in said wheel body to provide an output signal proportional tothe rate of rotation of said wheel; c) sensor to determine groundcontact of said wheel and an angle between the touch-down direction ofsaid wheel and the actual direction of travel of a user; and d) anelectronic control mounted in said wheel body and operably connected tosaid transducer and said sensor to determine the actual speed of travelof a user.
 21. A method for determining the rate of travel or the traveldistance of a user of roller skates or roller boards, comprising: a)determining the rate of rotation of a wheel of the roller skates orroller boards; b) determining the angle between the touch-down directionof the wheel and the actual direction of travel of a user; c)determining ground contact of the wheel; and d) determining the rate oftravel or the travel distance of the user from the rate of rotation ofthe wheel, ground contact of the wheel and the angle between thetouch-down direction of the wheel and the actual direction of travel ofa the user.
 22. A method as in claim 21, wherein: a) said determiningground contact is implemented by recording a measurement curvedescribing the rotational speed of the wheel; and b) determining groundcontact from kinks in the measurement curve.